1. Field of the Invention
The present invention relates to a device for driving lifting rollers in a creel stand in a spinning machine for treatment of slivers from a plurality of cans, such as a drawing frame and a roving frame.
2. Description of Related Art
It is well known that a drawing frame is for doubling a plurality of slivers from respective cans supplied to a corresponding drafting part to produce a more even sliver at the drafting part. The drawing frame is provided with a creel provided with a plurality of lifting rollers for taking out respective slivers from respective cans. The sliver cans for supplying the corresponding draft part are arranged along a single line. Namely, a plurality of the lifting rollers are arranged on the creel at positions spaced along this line. The slivers from the cans are taken out therefrom by the rotation of the respective lifting rollers toward the drafting part.
In the prior art, a single electric motor for driving the lifting rollers is provided. In this case, a difference in the tension of slivers taken out from the respective cans is, even if it is very small, created between the cans due to the change in the length of the sliver and weight. Namely, so long as the peripheral speed of the lifting rollers are the same for all of the cans, the farther a can is located away from the drafting part, the larger the tension of the sliver from the corresponding can. As a result, the longer the distance from the main part the higher the tension of the slivers taken out from the respective cans. The larger the tension of the slivers, the larger the elongation of the slivers. In other words, the farther a can is located away from the draft part the larger the amount of sliver remaining in a can will be wasted when the sliver from the nearest can is exhausted. As a result of a continuous increase in the remaining amount of sliver from the second cans to the last cans, the total amount of sliver remaining in the can is highly increased.
In order to obviate this difficulty, it can be conceived that a gearing of the train for driving the lifting rollers is such that the larger the rotational speed of the lifting rollers, the farther the cans are located away from the main part in such a manner that the tension of the slivers is equalized irrespective of the positions of the cans. In order to obtain an equalized tension, it may also be conceived to change the outer diameter between the lifting rollers in such a manner that the larger the outer diameter of the lifting rollers, the father the cans are located away from the main part. Furthermore, the Japanese Un-Examined Utility Model Publication No. 47-23301 discloses lifting rollers having tapered portions for holding slivers, and the contact positions of the slivers with the respective tapered portions are changed in such a manner that the slivers contact with the tapered portions at larger diameter points as the cans are located farther away from the drafting parts.
As is well known, the tension of the slivers during the drawing process should be controlled to a desired setting in accordance with process conditions, such as the characteristic of the fibers constructing the slivers, the weight of the slivers, and the speed of the drawing process. Namely, upon any change in the drawing conditions, it is essential to control the tension of the slivers to a desired value by varying the speed of the slivers introduced into the drafting parts. Upon such adjustment of the sliver tension, in order to maintain a constant tension of the slivers, the above prior art require change in gear members in the driving chain or a change in the position of the contact of the slivers with respective taper portions of the lifting rollers, which is tedious and complicated, and can only provide a very limited range of adjustment in the tension. Furthermore, a large number of extra parts, such as sets of gear wheels for changing the speed of the lifting rollers, are required.